As species migrate in response to climate change and do so at different rates and dispersal directions, extra ecosystem disturbances might arise, leading to temporary local biodiversity increases – fuelling a net (global) downward trend.

Forecasting biodiversity decline (the ‘Anthropocene Extinction’) is one of the biggest challenges while assessing the urgency of anthropogenic climate change, as it depends on so many factors (and multiple synergistic extinction drivers). This graphs shows different model runs for a biodiversity-climate model, plotting the biodiversity response for three latitude-dependent climate zones: cold climate regions (blue), intermediate climate regions (green) and hot climate regions (red). Due to the arrival of migrating species in cold climate regions biodiversity might locally first increase in response to an average temperature rise, fuelling interspecies competition and increased extinctions.

Modelling biodiversity decline as a consequence of climate change is a challenging task of the scientific community. Firstly because it’s such an important subject, secondly because it’s such a complex climate response, depending on so many factors.

Yesterday we learned that including complex species’ interaction like competition following from dispersal differences to model projections, might actually increase biodiversity loss projections following a global average temperature rise.

Today we learn it’s also a time and latitude-dependent process: because species have different dispersal rates while migrating to reach their thermal optima, some zones may be filled up with (invasive) species – then increasing competition, then possibly increasing (endemic) extinctions.

The above graph illustrating this process comes from a biodiversity-climate model study published in Nature Climate Change in 2012, conducted by a group of five ecologists led by Jon Norberg of Stockholm University – that also includes Mark Urban, lead author of the study about the net detrimental effects of different dispersal rates for different species that we addressed in part 7 of this series.

The Nature Climate Change publication adds the component of evolution to that equation, as another (inter)species response influencing the biodiversity development under climate change.

Biodiversity: instant decline in hot regions, delayed decline in cold regions

As there is a net migration of species away from hot regions, in these climate zones biodiversity decline is immediate and evolutionary responses are dominant. In both intermediate and cool climate regions net immigration of species first leads to a biodiversity increase (invasive species on top of a net downward biodiversity trend) and interspecies competition is the dominant factor over the evolutionary response to climate change:

“We demonstrate that both dispersal and evolution differentially mediate extinction risks and biodiversity alterations through time and across climate gradients. Together, high genetic variance and low dispersal best minimized extinction risks. Surprisingly, high dispersal did not reduce extinctions, because the shifting ranges of some species hastened the decline of others.”

“Evolutionary responses dominated during the later stages of climatic changes and in hot regions. No extinctions occurred without competition, which highlights the importance of including species interactions in global biodiversity models.”

‘Eco-climate inertia’ – after climate stabilisation biodiversity keeps declining

The model study further shows the large time lag of the biodiversity response to an initial (then stabilising) rise in average temperatures – adding yet another delaying factor to the already very complex and troublesome nature of Earth system climate inertia:

“Most notably, climate change created extinction and evolutionary debts, with changes in species richness and traits occurring long after climate stabilization. Therefore, even if we halt anthropogenic climate change today, transient eco-evolutionary dynamics would ensure centuries of additional alterations in global biodiversity.”

© Rolf Schuttenhelm | www.bitsofscience.org